Most prior boomerangs have been monolythically constructed of a relatively rigid material such as wood, metal or plastic. Although incidents of injury resulting from these rigid boomerangs are rare, there is a current desire on the part of both parents and toy manufacturers to make toys safer. Two ways to make a boomerang safer are to reduce its weight and rigidity. A combination of both is particularly desirable. Unfortunately boomerangs constructed monolythically from soft, resilient materials do not posses sufficient stiffness to maintain proper aerodynamic shape during flight.
Liston, U.S. Pat. No. 3,565,434, described boomerangs which were constructed with an internal wire framework covered by an outer material which was lighter in weight and less rigid. Liston stressed the fact that the framework was deformable, thus permitting adjustment of the boomerang's flight characteristics.
The present inventor has constructed several boomerangs using Liston's method and found that a metal wire framework has several limitations which are listed below:
a. If maleable metal wire is used (as suggested by Liston) it has a tendency to deform upon impact and spoil the characteristics of subsequent flights unless the boomerangs is re-formed. This re-forming is often beyond the skill of a child.
b. If the framework is made from hardened metal wire (such as spring steel) adjustment becomes quite difficult, especially when the outer covering is made from a soft material. Furthermore, hardened wire is more susceptable to break and leave a sharp edge which can protrude through the outer covering.
c. When the outer covering is made from very soft resilient materials, such as polyethylene foam or polyurethane foam, the wire framework does not provide adequate support for the broader areas of the boomerang-unless the framework contains many wire elements, which would be excessively heavy and costly to manufacture.
d. A wire framework tends to concentrate impact loads in too small an area. This leads to local material failure in the outer covering.